Method of manufacturing thin-film structure

ABSTRACT

A manufacturing method of a thin-film structural body, capable of preparing a thin-film structural body by using a sacrifice film without any protruding part on its surface, thereby preparing a thin-film structural body having high strength and reliability. After a sacrifice film is formed with a film thickness greater than a predetermined value, the surface of the sacrifice film is ground so that the surface of the sacrifice film is flattened with the film thickness of the sacrifice film being adjusted to the predetermined value. Thus, the influence of the surface irregularity of a substrate is eliminated and the surface of the sacrifice film is flattened. Thereby, a mass body, beams and fixed electrodes of a semiconductor acceleration sensor are prepared by using the sacrifice film.

TECHNICAL FIELD

The present invention relates to a manufacturing method of a thin-filmstructural body formed by using a semiconductor processing technique.

BACKGROUND ART

FIG. 13 is a cross-sectional view showing a thin-film structural bodyformed by using a conventional manufacturing method of a thin-filmstructural body. As shown in FIG. 13, this thin-film structural body101, which is provided with a supporting part 103 and a floating part105 supported by the supporting part 103, is formed above a substrate107 by using a conductive material. The floating part 105 is placed witha predetermined distance from the substrate 107, and sticks out outwardfrom an upper portion of the supporting part 103.

The substrate 107 is provided with a substrate main body 111, a firstinsulating film 113 formed on the substrate main body 111, a wiring 115selectively formed on the insulating film 113, and a second insulatingfilm 117 selectively covering a surface of the wiring 115 and theinsulating film 113.

The surface of the insulating film 113 is flat, and the wiring 115 isformed on the surface to protrude therefrom. The supporting part 103 isformed on the wiring 115 in a manner so as to cover one portion of thewiring 115. A hole 117 a is formed in the corresponding portion of theinsulating film 117 on which the supporting part 103 is to be formed sothat the supporting part 103 is connected to the wiring 115 through thehole 117 a. The film thickness of the insulating film 117 is made thinto such an extent that a step difference that is caused on the surfaceof the substrate 107 by the influence of the circumferential edge of theinsulating film 117 becomes substantially ignorable.

In the conventional manufacturing method of a thin-film structural body,first, a sacrifice film 121 is formed on the substrate 107 having such aconfiguration as shown in FIG. 14. Next, a portion of the sacrifice film121 at which the supporting part 103 is to be formed is partiallyremoved so that, as shown in FIG. 15, an anchor hole part 121 a isformed.

Successively, a thin-film layer 123 is deposited on the surface of thesacrifice film 121 and the surface of the substrate 107 exposed throughthe anchor hole part 121 a by using a conductive material, as shown inFIG. 16.

Next, the thin-film layer 123 is selectively removed and patterned sothat residual portions of the thin-film layer 123 form a thin-filmstructural body 101. In this case, a portion which has been fitted intoanchor hole part 121 a of the residual portion forms the supporting part103, and another portion located on the sacrifice film 121 forms thefloating part 105. Then, the sacrifice film 121 is removed so that astructure shown in FIG. 13 is obtained.

In such a conventional manufacturing method, in a state shown in FIG.14, a protruding part 122 a is formed on the surface 122 of thesacrifice film 121 due to the wiring 115 of the substrate 107. When sucha sacrifice film 121 having the protruding part 122 a is used forpreparing the thin-film structural body 101, the following problems areraised.

The protruding part 122 a has a slanting portion H which is locatedabove the outer edge of the wiring 115 and which approaches thesubstrate 107 in a direction toward the outside of the wiring 115. Withrespect to the thickness of the supporting part 103, there is alimitation in that if it is too thick, reduction of space is notavailable, and in that if it is too thin, there might be a failure inthe electrical connection between the thin-film structural body 101 andthe wiring 115. Moreover, with respect to the width of the wiring 115,it needs to be thinner in order to save space, depending on its layoutpositions and purposes of use. For this reason, in the case of the widthof the wiring 115 which is made thinner, the supporting part 103 isformed on the wiring 115 with a thickness that is almost the same as thewidth of the wiring 115 as shown in FIG. 13. In a corresponding manner,the anchor hole part 121 a is also formed on the wiring 115 with anopening width which is almost the same as the width of the wiring 115.As a result, as shown in FIG. 15, at least one portion of the slantingportion H remains on the peripheral portion 121 b of the anchor holepart 121 a of the sacrifice film 121.

The surface shape of this peripheral portion 121 b is reflected to theshape of the thin-film structural body 101 so that a neck portion 131 isformed at a portion corresponding to the peripheral portion 121 of thethin-film structural body 101, more specifically, a coupling portionbetween the supporting part 103 and the floating part 105, as shown inFIG. 13. For this reason, the thin-film structural body 101 might bedamaged at the neck portion 131 by an impact or the like, resulting indegradation in the strength and reliability of the thin-film structuralbody 101.

DISCLOSURE OF THE INVENTION

The present invention has been devised to solve the above-mentionedproblems, and an object thereof is to provide a manufacturing method ofa thin-film structural body, capable of preparing a thin-film structuralbody by using a sacrifice film without any protrusion on its surface,thereby preparing a thin-film structural body having high strength andreliability.

According to a first aspect of a manufacturing method of a thin-filmstructural body in accordance with the present invention, in themanufacturing method of a thin-film structural body including: asupporting part (23 b, 25 a) formed on a substrate (1); and a floatingpart (21, 23 a, 25 b, 25 c) integrally formed with the supporting part,supported by the supporting part and placed with a predetermineddistance from the substrate, the manufacturing method includes the stepsof: forming a sacrifice film (51) on the substrate with a film thicknessgreater than a predetermined value corresponding to the predetermineddistance; flattening a surface of the sacrifice film; forming an anchorhole part (51 a) by selectively removing a portion of the sacrifice filmon which the supporting part is to be formed; depositing a thin-filmlayer (53) on the sacrifice film and the substrate exposed through theanchor hole part; selectively removing and patterning the thin-filmlayer so that a residual portion of the thin-film layer is allowed toform the thin-film structural body (21, 23, 25); and removing thesacrifice film.

According to this aspect, after a sacrifice film is formed with a filmthickness greater than a predetermined value, the surface of thesacrifice film is flattened; therefore, the flattening process of thesurface of the sacrifice film can be carried out without being adverselyaffected by the irregularity on the surface of the substrate.Consequently, since the thin-film structural body can be prepared byusing the sacrifice film having a flat surface, it is possible toprevent an undesired nick portion from being formed in the thin-filmstructural body due to the irregularity of the surface of the sacrificefilm, and consequently to improve the strength and reliability of thethin-film structural body.

According to a second aspect of the manufacturing method of a thin-filmstructural body in accordance with the present invention, in the step offlattening the surface of the sacrifice film, the surface of thesacrifice film is ground.

According to a third aspect of the manufacturing method of a thin-filmstructural body in accordance with the present invention, in the step offlattening the surface of the sacrifice film, the film thickness of thesacrifice film is adjusted to a value which is equal to thepredetermined value.

According to a fourth aspect of the manufacturing method of a thin-filmstructural body in accordance with the present invention, in the step ofdepositing the thin-film layer, the thin-film layer is deposited with afilm thickness greater than the film thickness of the sacrifice filmwhich has been flattened.

According to this aspect, since the film thickness of the thin-filmlayer is set to be greater than the film thickness of the sacrifice filmwhich has been flattened so that the inside of the anchor hole part iscompletely filled with the thin-film layer. With this arrangement, it ispossible to prevent the edge of an opening of the anchor hole part ofthe sacrifice film from causing a reduction in the thickness of theportion of the thin-film structural body corresponding to the edge, andresulting in degradation in the strength.

According to a fifth aspect of the manufacturing method of a thin-filmstructural body in accordance with the present invention, the substrateincludes a wiring (41, 43, 45) formed in a manner so as to protrude fromthe surface of the substrate, the supporting part and the floating partare made from a conductive material, and the supporting part is formedon the wiring so as to be electrically connected to the wiring.

According to this aspect, it is possible to flatten the surface of thesacrifice film by eliminating adverse effects from the wiring on thesubstrate, and consequently to prevent a neck portion from being formedin the coupling portion between the supporting part and the floatingpart of the thin-film structural body, which has raised a problem in theabove-mentioned conventional technique.

According to a sixth aspect of a manufacturing method of a thin-filmstructural body in accordance with the present invention, in themanufacturing method of a thin-film structural body including: aconductive supporting part (23 b, 25 a) formed on a wiring (41, 43, 45)formed on a surface of a substrate (1); and a conductive floating part(21, 23 a, 25 b, 25 c) supported by the supporting part and placed witha predetermined distance from the substrate, the manufacturing methodincludes the steps of: forming a groove (33 a) having a depth of notless than the film thickness of the wiring on the surface of thesubstrate corresponding to at least a portion of the wiring placed belowthe supporting part; forming the wiring on the surface of the substrateon which the groove has been formed; forming a sacrifice film (51)covering the surface of the wiring and the surface of the substrate;forming an anchor hole part (51 a) by selectively removing a portion ofthe sacrifice film on which the supporting part is to be formed;depositing a thin-film layer (53) by using a conductive material on thesacrifice film and the substrate exposed through the anchor hole part;selectively removing and patterning the thin-film layer so that residualportions of the thin-film layer are allowed to form the thin-filmstructural body (21, 23, 25); and removing the sacrifice film.

According to this aspect, at least a portion of the wiring on which thesupporting part is to be provided is embedded in the groove having adepth of not less than the film thickness of the wiring provided on thesurface of the substrate; therefore, it is possible to prevent aprotruding part being formed on the surface of the substrate at theportion on which the supporting part is to be provided. Consequently, itbecomes possible to form a sacrifice film having a surface without anyprotruding part at a portion on which the supporting part is to beprovided without the necessity of carrying out a complex process on thesacrifice film, e.g., a flattening process. Moreover, the application ofthis sacrifice film for preparing a thin-film structural body makes itpossible to prevent a neck portion from being formed at the couplingsection between the supporting part and the floating part of thethin-film structural body, which has raised a problem in theconventional technique, and consequently to improve the strength andreliability in the thin-film structural body.

According to a seventh aspect of the manufacturing method of a thin-filmstructural body in accordance with the present invention, in the step ofdepositing the thin-film layer, the thin-film layer is deposited with afilm thickness greater than the film thickness of the sacrifice film.

According to this aspect, since the film thickness of the thin-filmlayer is set to be greater than the film thickness of the sacrificefilm, the inside of the anchor hole part is completely filled with thethin-film layer. With this arrangement, it is possible to prevent theedge of an opening of the anchor hole part of the sacrifice film fromcausing a reduction in the thickness of the portion of the thin-filmstructural body corresponding to the edge, and resulting in degradationin the strength.

According to an eighth aspect of the manufacturing method of a thin-filmstructural body in accordance with the present invention, the depth ofthe groove is set to be equal to the film thickness of the wiring.

According to this aspect, since the depth of the groove is set to beequal to the film thickness of the wiring, it is possible to flatten thesurface of the substrate without the necessity of particularly carryingout a flattening process on the portion on which the supporting part isto be provided.

According to a ninth aspect of the manufacturing method of a thin-filmstructural body in accordance with the present invention, the step offorming the wiring includes the steps of: depositing a conductive film(55) on the substrate having the groove with the same film thickness asthe depth of the groove by using the same material as the wiring; andpatterning the conductive film so as to remove a portion of theconductive film other than a portion (55 a) located inside the groovewith a predetermined gap dimension (F) from each of the side edges ofthe groove so that the residual portion is allowed to form the wiring.

According to this aspect, since the portion of the conductive filmformed on the substrate, located inside the groove with a predeterminedgap dimension from each of the side edges of the groove, is left, withthe other portion being removed, and the residual portion of theconductive film is allowed to form the wiring so that it is possible toform the wiring with a uniform film thickness, and consequently tofurther flatten the surface of the sacrifice film by flattening thesurface of the substrate.

According to a tenth aspect of the manufacturing method of a thin-filmstructural body in accordance with the present invention, the thin-filmstructural body forms at least one portion of a sensor part (3) which isinstalled in an acceleration sensor and which has a function ofdetecting acceleration.

According to this aspect, it is possible to improve endurance of thesensor part against an impact which is caused, for example, when theacceleration sensor is dropped, and consequently to improve strength andreliability of the acceleration sensor.

According to an eleventh aspect of the manufacturing method of athin-film structural body in accordance with the present invention, atleast one portion of a circumferential edge of the supporting part (23b) is placed above an outer edge of the wiring (43, 45), and thefloating part (23 a) sticks out from the one portion of the supportingpart and extends in a direction departing from the outer edge of thewiring.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent in conjunction with the followingdetailed and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a configuration of a main part of asemiconductor acceleration sensor to which a manufacturing method of athin-film structural body according to embodiment 1 of the presentinvention is applied;

FIG. 2 is a cross-sectional view taken along line A—A of FIG. 1;

FIGS. 3 to 6 are cross-sectional views showing manufacturing processesof the structure shown in FIG. 2.

FIG. 7 is a cross-sectional view taken along line A—A of FIG. 1, whichshows a case where a manufacturing method of a thin-film structural bodyof embodiment 2 of the present invention is applied to the accelerationsensor shown in FIG. 1;

FIGS. 8 to 12 are views showing manufacturing processes of a structureshown in FIG. 7;

FIG. 13 is a cross-sectional view showing a structure of a thin-filmstructural body formed by a conventional manufacturing method of athin-film structural body; and

FIGS. 14 to 16 are cross-sectional views showing manufacturing processesof the thin-film structural body shown in FIG. 13.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1

As shown in FIGS. 1 and 2, a semiconductor acceleration sensor to whicha manufacturing method of a thin-film structural body of embodiment 1 ofthe present invention is applied is provided with a substrate 1 servingas a sensor substrate, and a sensor part 3 which is formed on thesubstrate 1 and which has a function of detecting acceleration.

As shown in FIG. 1, the sensor part 3 is provided with a mass body 21functioning as a movable electrode, a plurality of fixed electrodes 23and a plurality of beams 25. The mass body 21, the fixed electrodes 23and the beams 25, which correspond to a thin-film structural body of thepresent invention, are formed by a conductive material, e.g., dopedpolysilicon which is formed by doping an impurity, e.g., phosphorus inpolysilicon.

The mass body 21, which is placed with a predetermined distance D fromthe substrate 1, has a plurality of movable electrode portions 21 aextending in a direction C which is perpendicular to direction B ofacceleration to be detected. The beams 25, which are integrally formedwith the mass body 21, has a function of suspending the mass body 21above the substrate 1 movably in direction B with a restoring force.Each of the beams 25 is provided with a supporting part 25 a protrudingfrom the substrate 1, a coupling portion 25 b to the supporting part 25a, and a spring portion 25 c provided between the coupling portion 25 band the end edge of the mass body 21 with respect to direction B. Thisspring portion 25 c is elastically bent and deformed so that thedistance between the coupling portion 25 b and the mass body 21 indirection B is expanded and reduced.

In such a configuration of the mass body 21 and the beams 25, the massbody 21, and the spring portion 25 c and the coupling portion 25 b andthe beams 25 correspond to the floating part of the thin-film structuralbody according to the present invention.

The respective fixed electrodes 23 are placed along direction C withpredetermined distances in direction B between each other. Moreover,each fixed electrode 23 is provided with a fixed electrode portion 23 bforming a floating part which is placed with a predetermined distance Dfrom the substrate 1, and a supporting part 23 b supporting the fixedelectrode portion 23 a.

The fixed electrode portions 23 b of the respective fixed electrodes 23and the movable electrode portions 21 a of the mass body 21 arealternately placed with distances from each other in direction B,thereby forming a capacitor. Thus, acceleration is detected based uponcapacity changes in the capacitor that are generated due to shifts ofmovable electrode portions 21 a.

As shown in FIGS. 1 and 2, the substrate 1 is provided with a substratemain body 31 formed by a semiconductor such as silicon, an oxide film 33serving as a first insulating film formed on the substrate main body 31,a plurality of wirings 41, 43, 45 selectively formed on the oxide film33, and a nitride film 47, which serves as a second insulating film,selectively covering the surface of the wirings 41, 43, 45 and thesurface of the oxide film 33.

The wiring 41 is provided with an exposed portion 41 a placed on thesubstrate 1 in an exposed state at an opposing area which faces the massbody 21 of the substrate 1, and a contact portion 41 b placed below thesupporting part 25 a and electrically connected to the supporting part25 a. The wirings 43, 45, which are used for drawing signals from thefixed electrodes 23, are connected to the respective fixed electrodes 23through the contact portions 43 a, 45 a.

In a corresponding manner, the nitride film 47 has a window portion 47 aand holes 47 b and 47 c. The exposed portion 41 a of the wiring 41 isexposed to the substrate 1 through the window portion 47 a, and thecontact portion 41 a is electrically connected to the supporting part 25a. The contact portions 43 a, 45 a of the wirings 43, 45 areelectrically connected to the fixed electrodes 23 through the holes 47b, 47 c.

In the semiconductor acceleration sensor having the above-mentionedarrangement, in the present embodiment, the wirings 41, 43, 45 areformed on the flat surface of the oxide film 33 in a manner so as toprotrude therefrom. Moreover, the film thickness of the nitride film 47is made thin to such an extent that a step difference caused on thesurface of the substrate 1 by the influence of its circumferential edgebecomes substantially ignorable. Therefore, the portions of the surfaceof the substrate 1 on which the wirings 41, 43, 45 are formed areallowed to protrude upward from the other portions by an amountcorresponding to the film thickness of each of the wirings 41, 43 45.

Moreover, with respect to the thickness of the supporting part 25 a, 23b, there is a limitation in that if it is too thick, reduction of spaceis not available, and in that if it is too thin, there might be afailure in the electrical connection between the mass body 21 and thewiring 41 through the beams 25 and the electrical connection between thefixed electrodes 23 and the wirings 43, 45. Moreover, with respect tothe width of the wirings 43, 45, it is made thinner in order to savespace. For this reason, the supporting part 23 b of the fixed electrodes23 are formed on the wirings 43, 45 with a thickness that is almost thesame as the width of the wirings 43, 45. As a result, at least oneportion of the circumferential edge of the supporting part 23 b islocated above the outer edges of the wirings 43, 45. Moreover, the fixedelectrode portions 23 a are allowed to stick out from the one portionand extend in a thin rod state in a direction departing from the edge ofthe wirings 43, 45. Here, the mass body 21 and the beams 25 are formedin an area surrounded by the outer edge of the wiring 41.

In accordance with such a configuration of the semiconductoracceleration sensor 1, in the present embodiment, the mass body 21, thebeams 25 and the fixed electrodes 23 are prepared in the followingmanufacturing method.

First, as shown in FIG. 3, a sacrifice film 51 is formed on thesubstrate 1. In this case, the film thickness E of the sacrifice film 51is set to a value approximately two times the distance D between thesubstrate 1 and the mass body 21 as well as the fixed electrode portions23 a. The sacrifice film 51 is formed by an oxide film, PSG or BPSG, forexample.

Successively, an etching back process which grinds the surface of thesacrifice film 51 is carried out so that, as shown in FIG. 4, thesurface of the sacrifice film 51 is flattened and the film thickness Eof the sacrifice film 51 is adjusted to a value which is equal to thedistance D.

Then, portions of the sacrifice film 51, in which the supporting parts25 a, 23 b are to be formed, are selectively removed to form anchor holeparts 51 a. Thus, a structure shown in FIG. 5 is obtained. At this time,on the bottom of the anchor hole part 51 a, the contact portions 41 b,43 a, 45 a of the wirings 41, 43, 45 are exposed through the windowportion 47 a and the holes 47 b, 47 c of the nitride film 47.

As shown in FIG. 6, a thin-film layer 53 is deposited on the residualsacrifice film 51 and the substrate 1 exposed through the anchor holepart 51 a by using a conductive material, e.g., doped polysilicon. Thefilm thickness of this thin-film layer 53 is set to a value greater thanthe film thickness E of the sacrifice film 53 which has been flattened.As a result, the inside of the anchor hole part 51 a is completelyfilled with the thin-film layer 53.

Successively, the thin-film layer 53 is selectively removed andpatterned so that residual portions of the thin-film layer 53 areallowed to form the mass body 21, the beams 25 and the fixed electrodes23. In this case, portions of the residual portions, which have beenfitted into the inside of the anchor hole part 5 la, are allowed to formthe supporting parts 25 a, 23 b, and portions located on the sacrificefilm 51 are allowed to form the mass body 21, the spring portion 25 c,the coupling portions 25 b and the fixed electrode portions 23 a. Then,the sacrifice film 51 is removed so that a structure shown in FIGS. 1and 2 is obtained.

As described above, according to the present embodiment, after thesacrifice film 51 has been formed with a film thickness E greater than apredetermined value, the surface of the sacrifice film 51 is ground sothat the surface of the sacrifice film 51 is flattened with the filmthickness E of the sacrifice film 51 being adjusted to a predeterminedvalue; thus, it becomes possible to flatten the surface of the sacrificefilm 51 with the influence of the irregularity of the surface of thesubstrate 1 being eliminated. As a result, since the mass body 21, thebeams 25 and the fixed electrodes 23 can be prepared by using thesacrifice film 51 having a flat surface, it is possible to prevent anundesired neck portion being formed on the mass body 21, the beams 25and the fixed electrodes 23 due to the irregularity of the surface ofthe sacrifice film 51, consequently to improve the strength andreliability of the sensor part 3.

In particular, each fixed electrode 23 is formed in a manner so as tobridge the outer edges of the wirings 43 and 45 at the connectingsection between the supporting part 23 b and the fixed electrode portion23 a; therefore, in the case where each fixed electrode 23 is preparedby the conventional manufacturing method, a neck portion is formed inthe connecting section between the fixed electrode portion 23 a and thesupporting part 23 b, causing degradation in the shock resistance of thefixed electrode 23. However, in accordance with the manufacturing methodof the present embodiment, the fixed electrodes 23 are prepared withoutcausing any neck portion, making it possible to improve the shockresistance of the fixed electrodes 23.

Moreover, since the film thickness of the thin-film layer 53 is set tobe greater than the film thickness E of the sacrifice film 51 which hasbeen flattened, the inside of the anchor hole part 51 a can be filledwith the thin-film layer 53. Therefore, it becomes possible to preventthe edge of an opening of the anchor hole part 51 a of the sacrificefilm 51 from causing a reduction in the thickness of the portion of thebeams 25 and the fixed electrodes 23 corresponding to the edge, andresulting in degradation in the strength.

Embodiment 2

The semiconductor acceleration sensor, which is prepared by using themanufacturing method of a thin-film structural body according to thepresent embodiment, is only different from the above-mentionedsemiconductor acceleration sensor shown in FIG. 1 and FIG. 2 in that thewirings 41, 43, 45 are substantially embedded in the surface of thesubstrate 1. Therefore, with respect to the semiconductor accelerationsensor to which the manufacturing method in accordance with the presentembodiment is applied, those constituent parts which are the same asthose of the semiconductor acceleration sensor shown in FIG. 1 and FIG.2 are indicated by the same reference numerals, and the descriptionthereof will not be repeated.

In the manufacturing method in accordance with the present embodiment,the wirings 41, 43, 45 are embedded in the surface of the substrate 1 sothat the surface of the substrate 1 is flattened, and by forming thesacrifice film 51 on the substrate 1, it becomes possible to obtain asacrifice film 51 having a flat surface without carrying out a specialtreatment, such as an etching back process, thereon. Referring to FIGS.7 to 12, the following description will be given of the contents of theembodiment in detail. FIG. 7 shows a state where the semiconductoracceleration sensor has been completed. It is noted that FIGS. 7 to 12only show a portion in which the wiring 43 of the wirings 41, 43, 45 isprepared.

First, an oxide film 33 is formed on a substrate main body 31, andgroove 33 a is formed in a portion corresponding to the wirings 41, 43,45 on the surface of the oxide film 33. Thus, a structure shown in FIG.8 is obtained.

Successively, a conductive film 55, used for forming the wirings 41, 43,45, is formed on the oxide film 33. Consequently, a structure shown inFIG. 9 is obtained. The material of this conductive film 55 is the sameas the material of the wirings 41, 43, 45, and its film thickness is setto the same as the depth of the groove 33 a.

Then, the conductive film 55 is selectively removed and patterned byusing a mask pattern which is not shown. A portion except for a portion55 a of the conductive film 55 located inside the groove 33 a with apredetermined gap dimension F from each of the side edges 33 b of thegroove 33 a is removed. Consequently, a structure shown in FIG. 10 isobtained. The wirings 41, 43, 45 are formed by this residual portion 55a. In this case, the surface of the wirings 41, 43, 45 and the surfaceof the oxide film 33 are located on the same plane.

In this manner, each of the wirings 41, 43, 45 is formed inside thegroove 33 a with a margin corresponding to the gap dimension F from eachof the side edges 33 b so that it is possible to form wirings 41, 43, 45having a flat surface with a uniform film thickness. The value of thegap dimension F is set to not more than 0.5 μm, e.g., 0.3 μm. In thiscase, a gap 57 corresponding to the dimension F is provided between thecircumferential portion of each of the wirings 41, 43, 45 and each ofthe side edges 33 b of the groove 33 a.

It is noted that, in an attempt to obtain a sufficient effect bypreventing a protruding part from being formed on the surface of thesubstrate 1 due to the influence of each of the wirings 41, 43, 45, thedepth of the groove 33 a may be set to a value greater than the filmthickness of each of the wirings 41, 43, 45. In this case, the surfaceof each of the wirings 41, 43, 45 is located below the surface of theoxide film 33; however, this arrangement makes it possible to prevent aprotruding part from being formed on the surface of the substrate 1 dueto the influence of each of the wirings 41, 43, 45.

Successively, a nitride film 47 is formed on the entire surface area ofthe substrate 1 in a manner so as to cover the wirings 41, 43, 45. Thus,a structure shown in FIG. 11 is obtained. At this time, the inside ofthe gap 57 is filled with the nitride film 47. Successively, the nitridefilm 47 is selectively removed by using a mask pattern which is notshown; thus, a window portion 47 a and holes 47 b, 47 c are formed.

Here, the film thickness of the nitride film 47 is made thin to such anextent that a step difference caused on the surface of the substrate 1by the influence of its circumferential edge becomes substantiallyignorable, and set to a uniform value. Consequently, the surface of thesubstrate 1 is set in a substantially flat state.

Successively, as shown in FIG. 12, a sacrifice film 51 is formed on thesubstrate 1 formed in this manner with a film thickness G. This filmthickness G is set to a predetermined value corresponding to a gap D.Since the surface of the substrate 1 is substantially flat, the surfaceof the sacrifice film is maintained in a flat state without thenecessity of a special treatment, e.g., an etching back process.

With respect to the succeeding processes, the same processes as thoseshown in FIGS. 5 and 6 are carried out; therefore, the descriptionthereof will be given briefly. After the sacrifice film 51 has beenformed as described above, portions of the sacrifice film 51 on whichthe supporting parts 25 a, 23 b are to be formed are selectively removedso that an anchor hole part 51 a is formed. Next, a thin-film layer 53is deposited on the residual sacrifice film 51 and the substrate 1exposed through the anchor hole part 51 a by using a conductivematerial, e.g., doped polysilicon. Successively, the thin-film layer 53is selectively removed and patterned so that residual portions of thethin-film layer 53 are allowed to form the mass body 21, the beams 25and the fixed electrodes 23. In this case, portions of the residualportions, which have been fitted into the inside of the anchor hole part51 a, are allowed to form the supporting parts 25 a, 23 b, and portionslocated on the sacrifice film 51 are allowed to form the mass body 21,the spring portion 25 c, the coupling portions 25 b and the fixedelectrode portions 23 a. Then, the sacrifice film 51 is removed so thata structure shown in FIG. 7 is obtained.

As described above, in accordance with the present preferred embodiment,the wirings 41, 43, 45 are embedded in the groove 33 a having the samedepth as the film thickness of the wirings 41, 43, 45 provided on thesurface of the substrate 1; therefore, it is possible to flatten thesurface of the substrate 1, and consequently to form a sacrifice film 51having a flat surface without the necessity of a complex flatteningtreatment to be carried out on the sacrifice film 51. Then, the massbody 21, the beams 25 and the fixed electrodes 23 are prepared by usingthis sacrifice film 51 so that the same effects as the above-describedembodiment 1 are obtained.

In particular, in the present embodiment, each of the wirings 41, 43, 45is formed with a margin corresponding to a gap dimension F from each ofthe side edges 33 b of the groove 33 a to the inside of the groove 33 aso that it is possible to form the wirings 41, 43, 45 having a flatsurface with a uniform film thickness. Consequently, even when thenitride film 47 is formed with a uniform film thickness, the surface ofthe substrate 1 is flattened more effectively so that the surface of thesacrifice film 51 is further flattened.

While the present invention has been described in detail, the abovedescription is illustrative in all aspects and the present invention isnot restricted thereto. It will be understood that numerous variantswhich are not illustrated can be supposed without departing from thescope of the invention.

1. A manufacturing method of a thin-film structural body including asupporting part formed on a substrate and a floating part integrallyformed with said supporting part, supported by said supporting part andplaced with a predetermined distance from said substrate, saidmanufacturing method comprising: forming a wiring on a part of saidsubstrate; forming a sacrifice film on said wiring and said substratewith a film thickness greater than said predetermined distance;flattening a surface of said sacrifice film; forming an anchor hole partby selectively removing a portion of said sacrifice film that coverssaid wiring on which said supporting part is to be formed; depositing athin-film layer on said sacrifice film and said wiring exposed throughsaid anchor hole part; selectively removing and patterning saidthin-film layer so that a residual portion of said thin-film layer formssaid thin-film structural body; and removing said sacrifice film,wherein said wiring is formed to protrude from a surface of saidsubstrate, said supporting part and said floating part are made from aconductive material, said supporting part is formed on said wiring so asto be electrically connected to said wiring, at least one portion of acircumferential edge of said supporting part is placed above an outeredge of said wiring, and said floating part is connected to said atleast one portion of said supporting part and extends in a directiondeparting from the outer edge of said wiring.
 2. The manufacturingmethod of a thin-film structural body according to claim 1, wherein insaid flattening of the surface of said sacrifice film, the surface ofsaid sacrifice film is ground.
 3. The manufacturing method of athin-film structural body according to claim 2, wherein in saidflattening of the surface of said sacrifice film, said film thickness ofsaid sacrifice film is adjusted to a value which is equal to saidpredetermined distance.
 4. The manufacturing method of a thin-filmstructural body according to claim 3, wherein in said depositing of saidthin-film layer, said thin-film layer is deposited with a film thicknessgreater than a film thickness of said flattened sacrifice film.
 5. Themanufacturing method of a thin-film structural body according to claim1, wherein said thin-film structural body forms at least one portion ofa sensor part which is installed in an acceleration sensor and which hasa function of detecting an acceleration.
 6. A manufacturing method of athin-film structural body including a conductive supporting part formedon a wiring formed on a surface of a substrate and a conductive floatingpart supported by said supporting part and placed with a predetermineddistance from said substrate, said manufacturing method comprising:forming a groove having a depth equal to a film thickness of saidwiring, said groove being formed on the surface of said substrate andcorresponding to at least a portion of said supporting part; formingsaid wiring in said groove to obtain a flat surface of said substrate;forming a sacrifice film covering a surface of said wiring and saidsurface of said substrate; forming an anchor hole part by selectivelyremoving a portion of said sacrifice film on which said supporting partis to be formed such that a portion of said wiring is exposed;depositing a thin-film layer on said sacrifice film and said portion ofwiring exposed through said anchor hole part, said thin-film layercomprising a conductive material; selectively removing and patterningsaid thin-film layer so that residual portions of said thin-film layerform said thin-film structural body; and removing said sacrifice film.7. The manufacturing method of a thin-film structural body according toclaim 6, wherein in said depositing of said thin-film layer, saidthin-film layer is deposited with a film thickness greater than a filmthickness of said sacrifice film.
 8. The manufacturing method of athin-film structural body according to claim 6, wherein said forming ofsaid wiring includes: depositing a conductive film on said substratehaving said groove with a film thickness equal to said depth of saidgroove by using the same material as said wiring; and patterning saidconductive film to remove a portion of said conductive film other than aportion located inside said groove, with a predetermined gap dimensionfrom each side wall of said groove so that a residual portion of saidconductive film forms said wiring.
 9. The manufacturing method of athin-film structural body according to claim 6, wherein said thin-filmstructural body forms at least one portion of a sensor part which isinstalled in an acceleration sensor and which has a function ofdetecting an acceleration.
 10. The manufacturing method of a thin-filmstructural body according to claim 8, wherein at least one portion of acircumferential edge of said supporting part is placed above an outeredge of said wiring, and said floating part is connected to said atleast one portion of said supporting part and extends in a directiondeparting from the outer edge of said wiring.